In this project the investigators plan to extend ongoing studies in the drug treatment of primarily nonendogenous depression. Emphasis will be placed on identifying subgroups of patients with depessive neuroses who respond preferentially to one or the other antidepressant drug class. Using established clinical and biochemical methodology, carefully clinical trials will be conducted in outpatient populations suffereing from depression with varying admixtures of anxiety, hypochodriasis and somatic complaints. Comparisons will be made between prototypic monoamine oxidase inhibitors and tricyclic antidepressant drugs and monitoring techniques for defining optimal dosage in individual patients will be investigated. The relationship of phenelzine biotransformation to therepeutic response will be examined as well as the relationship of acetylator phenotype to in vivo platelet MAO inhibition achieved at a clinically effective dose. Multivariate statistical techniques including discriminant function, factor and custer analytic studies will be carried out utilizing both symptom self-rating (SCL-90) and structured depression interview data. Longterm follow-up studies of patients treated for depressive neurosis will be conducted in our study population from clinical trials conducted over the period 1970-1975.